This invention relates to a mixing system for mixing two separate components or constituents, and more particularly to an apparatus and method for an eductor system for mixing two separate components one of which is a liquid.
An eductor mixer system is effective in continuously mixing two separate constituents such as liquids and particulate materials to form a slurry. The term xe2x80x9cslurryxe2x80x9d is interpreted herein as including dispersions and solutions. The term xe2x80x9cparticulate materialxe2x80x9d is interpreted herein for all purposes as including granular materials, powdered materials, and other pressure fluidizable transportable materials. The eductor mixer system thoroughly mixes the liquid with the particulate material and obtains a relative high negative pressure or vacuum level which is efficiently generated to positively draw or suck the particulate material into the eductor system. The working liquid fluid is directed through a nozzle to produce a high velocity. The high velocity liquid stream creates a low pressure region adjacent the downstream end of a nozzle for the particulate material. The low pressure zone causes the particulate material to be drawn or sucked through a suction port into a mixing chamber created by the swirling liquid stream adjacent the nozzle for the particulate material.
U.S. Pat. No. 4,186,772 issued Feb. 5, 1980 shows an eductor mixer system which is used to mix a powered solute with a liquid solvent. The eductor mixer system shown therein is effective in mixing continuous or batch preparations of a dry material with a liquid with the liquid working fluid being thoroughly and intimately mixed with the dry powdered solute. A relatively high vacuum or low pressure level is obtained to draw or suck the powered material into the system. While a relatively small gap or orifice is provided for a rapid acceleration of the working fluid flowing axially through the orifice in the ""772 patent, there is no showing or suggestion of providing a swirling action to the liquid prior to being mixed with the dry powdered material as an axial flow of the liquid working fluid is provided.
U.S. Pat. No. 4,884,925 issued Dec. 5, 1989 shows an eductor system in which a plurality of spray nozzles are provided for the liquid working fluid to wash and clean the inner peripheral surface of a hopper. A cylindrical pipe positioned within the hopper is provided for particulate material. The liquid working fluid discharged from the nozzles solves a problem in which dry hydratable solids were plugging the throat of the eductor to make frequent cleaning necessary. The swirling action in the hopper is provided to ensure all the surfaces of the hopper wall are washed with the liquid, not to create a suction at the end of the outlet pipe for the particulate material. The outlet pipe for the dry particulate material does not have a nozzle and a suction is applied to the lower end of the hopper, not at the lower end of the pipe for the dry particulate material.
It is desired that an eductor system for mixing two separate components, one of which is a liquid, be provided in which a liquid working fluid is directed into a swirling movement in a vortex chamber prior to contact and mixing with the other constituent or component so that a rapid and continuous intimate mixing of the liquid and other component is obtained in a mixing chamber adjacent the outlet nozzle for the other component.
The eductor system of the present invention is directed to an apparatus and method for the continuous mixing of a liquid with a separate component, such as another liquid or a particulate material. When the separate component is particulate material, a slurry is formed. The term xe2x80x9cslurryxe2x80x9d is interpreted herein for all purposes as including solutions and dispersions. The term xe2x80x9cparticulate materialxe2x80x9d is interpreted herein for all purposes as including granular and powdered materials or other pressure transportable or fluidizable materials. The liquid is the working fluid which provides the motive fluid power and is first directed into the annulus of a vortex chamber in which a swirling vortex movement of the liquid is created prior to mixing with the dry particulate material. A conduit for the dry particulate material is mounted within the vortex chamber and has an inner discharge nozzle at the end of the conduit. A restriction or constriction is formed between the outer surface of the inner nozzle and a concentric outer nozzle forming the inner peripheral surface of the vortex chamber through which the swirling liquid flows at an increased velocity to create a suction at the lower end of the dry particulate conduit to suck or draw the particulate material from the conduit for mixing. A mixing chamber is defined below the coaxial nozzles and the swirling liquid mixes with the dry particulate material to form a slurry. The slurry may be transported to a suitable predetermined location for storage or use.
To provide a swirling movement to the liquid, the vortex chamber is formed of a generally cylindrical shape and a liquid supply conduit extends in a perpendicular direction to the longitudinal axis of the cylindrical vortex chamber. The entrance opening for the liquid to the vortex chamber is adjacent the inner peripheral surface of the vortex chamber and tapers to conform to the peripheral surface of the vortex chamber with the liquid being directed along the inner peripheral surface of the vortex chamber for creating a swirling liquid stream in the vortex chamber. The liquid supply conduit changes from a circular cross section to a rectangular cross section at the entrance opening to the vortex chamber to provide a relatively smooth transition with minimal irregular motion. The cross sectional area of the tangential entrance opening for the liquid thus has a transition from a circular to rectangular shape that provides a thin layer or sheet of liquid fluid with a uniform pressure/velocity profile for entering the vortex chamber of the mixing apparatus. An annulus is provided in the vortex chamber between the outer surface of the vortex chamber and the conduit for the dry particulate material.
The liquid flow is the primary fluid flow and the suction flow of the particulate material is the secondary flow. The swirling motion of the liquid is a spinning helical motion. Swirl is the circumferential velocity component that will cause a fluid stream to rotate about its axis. Swirl changes energy momentum into centrifugal force that will cause a rotating stream to have three velocity components; a) axial, b) circumferential and c) radial. The circumferential velocity will move the heavier or more dense material (solids) or liquid to the outside while the radial velocity will move the lighter constituents to the inside toward the longitudinal axis. The introduction of swirl enhances mixing due in part to an increase in turbulence. Swirl imparts radial acceleration to particles, modifying their motion and dispersion behavior, and enhances interfacial contact between two or more constituents due to stretching, straining and folding of particles and droplets to form a uniform mixture. The total energy in a steadily flowing fluid is constant along its flow path and as the velocity of the fluid increases the pressure within the fluid decreases. The intense swirling motion of the pressurized liquid when it enters the vortex chamber provides a sheet of liquid that has a uniform pressure profile. When the liquid helical stream passes through a constriction, slower moving fluid adjacent the surfaces defining the constriction forms an energized boundary layer to reduce frictional drag or a shear layer resulting in a more efficient pressure recovery.
A diffuser structure defines an outer coaxial concentric outer nozzle about the inner nozzle of the conduit for the particulate material to provide a swirl mixing chamber downstream of the inner nozzle to effect intermingling of the liquid and dry particulate material for discharge into the mixing chamber. The diffuser structure includes an upper or upstream converging portion defining the outer coaxial nozzle, a small length cylindrical or throat portion, and a lower or downstream diverging portion. The outer coaxial nozzle is arranged about and in concentric relation to the nozzle of the particulate material conduit and defines an inner surface extending at a converging angle preferably about thirty (30) degrees relative to the longitudinal axis of the conduit to form a gap or constriction between the coaxial nozzle of the conduit and the diffuser structure. The cylindrical throat portion is of a relatively small length and the diverging outlet portion is preferably at an angle of about thirty (30) degrees relative to the longitudinal axis of the conduit. A relatively large mixing chamber is defined below the diverging portion.
A relatively narrow annular gap or constriction from the liquid is formed between the outer nozzle and the inner nozzle to provide an increase in the velocity of the downward moving liquid stream in a swirling helical path. The narrow annular gap provides a venturi effect and the pressurized liquid has a high velocity when flowing through the gap and the diffuser structure. The outer periphery of the discharge nozzle for the particulate material may be formed with a plurality of spaced slotted portions to form lobes which are effective in generating turbulence for the liquid flowing downward in a helical path from the vortex chamber past the gap between the nozzles. The lobes provide varying velocities to the liquid to effect increased interfacial contact between the liquid and the particulate material to provide a more efficient mixing. A swirling action imparts acceleration to particles modifying their motion and dispersion behavior. Improved mixing is attributed to the increased liquid and particulate material interaction formed in a vortex. Turbulent flow provides a mechanism for mixing a slower fluid near an inner wall surface with a faster fluid adjacent an outer wall surface. A turbulent boundary layer is more resistant to such a wall separation than a laminar layer. By accelerating the fluid near a wall surface, the character of the velocity profile becomes more negative, and wall separation is avoided.
The particulate material to be mixed with a liquid may comprise various materials and chemical additives, such as cement, oil well drilling muds, polymers, diatomaceous earth, talc, lime, paint pigments, powdered fire retardant materials, and other similar types of materials. Oftentimes, the particulate material is mixed with a liquid upon unloading of the particulate material from a container or other storage facility to form a slurry which may be transported to a predetermined location for use or for storage.
An object of the present invention is to provide an apparatus and method for an eductor system for the continuous mixing of a liquid with a separate component to form a generally uniform mixture.
A further object of the invention is to provide such an apparatus and method in which a liquid is first directed into a vortex chamber to provide a swirling vortex movement for subsequent mixing with another separate component to provide improved mixing of the liquid and separate component.
A further object of the invention is to provide such an apparatus and method in which a conduit for a particulate material extends axially within a vortex chamber and has a lower inner nozzle defining a gap between the inner nozzle and an outer concentric nozzle of the vortex chamber to increase the velocity of the liquid at the gap thereby to provide a suction for the particulate material for improved mixing of the liquid with the particulate material.
Another object of the invention is to provide an apparatus and method in which irregular surfaces are provided in the annular gap or constriction between the concentric coaxial nozzles to provide varying velocities in the liquid thereby to cause increased interfacial contact between the liquid and dry particulate material to provide a more efficient mixing.
Other objects include providing a passive method of energizing the fluid boundary layer in a conically shaped diffuser, providing a method to reduce viscous drag with a diffuser having a short throat, and providing a method that generates a vacuum with a nozzle fluid velocity of about 60 feet per second and an operating pressure drop of 25 psig.
Other objects, features, and advantages of the invention will become more apparent from the following specification and drawings.